1. Field of the Invention
The present invention relates generally to the degradation of polyurethane and more specifically to the enzymatic degradation of polyurethane.
2. Description of the Related Art
Polyurethanes are a diverse group of man-made polymers of considerable economic importance that have a wide range of chemical and physical properties. Polyurethane-based coatings, such as polyurethane paint, are used on many structures such as buildings, vehicles, boats, and aircraft. One of the main benefits of using polyurethane-based coatings is the environmental resistance of polyurethane. However, the environmental resistance also makes it difficult to remove.
Currently, polyurethane-based coatings are removed, for repair and repainting, using organic solvents such as methlyene chloride. However the use of methylene chloride creates large amounts of toxic waste. In fact, some uses of methylene chloride are banned in some States. Alternatively, polyurethane-based coatings are removed using blast cleaning with plastic beads. However, the blasting can damage some types of composite surfaces being cleaned. Moreover, the spent plastic beads create new waste disposal problems. Also, the polyurethane particles removed are not degraded to harmless components.
As an alternative, biological degradation of polyurethane has been proposed. Biological degradation of naturally-occurring polymers, such as chitin and cellulose, involves induction of hydrolytic enzymes by soluble oligomers released form the polymer surface. Through the oligomers, the hydrolytic enzymes break down the polymer into biologically digestible components. However, induction of enzymes for degrading a synthetic polyurethane-coated surface is more difficult because of the lack of soluble material (oligomers) released from weathered, painted surfaces. Accordingly, the direct use of microbes to degrade polyurethane coatings on surfaces is impractical.